Listening to the soft tok-tok-tok of the electric kettle heating water, I busily took out my notebooks and pens from my bag and arranged them on the desk. Kuronuma-san had been considerate enough earlier, but sharing one tiny folding umbrella between the two of us was impossible in the end, and both he and I ended up drenched by the rain… well, not completely soaked, but enough that our uniforms were wet to the point of feeling uncomfortable.
So now I was wearing my training jersey—top and bottom—and both my uniform and Kuronuma-san's hoodie were stuffed into the dryer that, for some reason, happened to be in the room. Kuronuma-san had changed into his spare hoodie too, and was now waiting for some coffee to warm himself up.
A click sounded as the kettle switched off, signalling that the water had boiled. I quietly stood up. Kuronuma-san had already taken out two mugs and the coffee grounds, so I scooped the grounds into the cups and slowly poured in the hot water.
With a swirl of white steam, the coffee grounds mixed with the water, releasing a rich, comforting aroma that instantly filled the room. To keep clumps from forming, I gently stirred the coffee with a spoon, then handed one of the mugs to Kuronuma-san.
"Thanks."
"It's fine. At least let me do something like this."
We smiled at each other, then each took a sip. The coffee was freshly brewed and hot enough to almost burn my tongue, but for our rain-chilled bodies, the heat felt surprisingly pleasant.
…Did I put too much powder in? It was a bit strong, and I ended up sticking my tongue out from the bitterness. Kuronuma-san chuckled a little at the sight.
"Well then, now that the coffee's ready, let's get started."
"Yes, thank you for today."
As I topped off my mug with a little more hot water, I bowed my head in reply to him saying we should begin soon. Since I was the one being taught, I had to be polite.
"What I'm teaching you—like I said before—is how to improve and develop a Uma Musume's distance aptitude."
"Yes!"
"So, what would you do? Before asking me, try thinking for yourself first."
Having been told that, I tried to think it out. In the app, if you want to change distance aptitude, you improve C to B, B to A through inheritance factors from the parent characters. But obviously, you can't do something so systematic in this world, so that's out.
Then, realistically, if you want to improve distance aptitude without inheritance like in the app, the only method I can think of is something like Mihono Bourbon from the anime—repeating hill-track training like a demon to extend the distance you can run.
But if you ask me why hill training increases running distance… I honestly have no idea. I never looked into it in my past life either.
Thinking simply, I'd imagine that if you want to run longer distances, doing stamina training to strengthen your cardiovascular endurance should be ideal. But in the app, stamina training is the pool, and hill training is listed as a "guts training" category, so you can't say one is strictly better than the other.
"If you don't know yet, that's fine. What's important is to not leave your questions unanswered. Think, learn, and grow from there."
Kuronuma-san said this as I struggled with my thoughts. I'd heard before that you grow more when you think and act consciously, instead of just doing what you're told.
Alright, let's think a bit more. Why is hill training in the "guts" category? Couldn't it also be stamina training?
Or rather—what exactly does hill training train?
The benefits of hill training are that, compared to running on flat ground, you get more efficient results for the same distance. Because the slope length is fixed, it naturally becomes interval training, making it easy to repeatedly apply appropriate loads for the Uma Musume.
During practical training, the instructor said that on the common 3–4% slopes used in hill tracks, the time per furlong is about 2–4 seconds slower than flat ground, yet provides the same level of strain. Being slower means less leg wear, reducing the risk of injury or illness—pure benefit for us Uma Musume.
However, if a young or inexperienced Uma Musume—without proper supervision from an instructor or trainer—tries hill training on her own, she might misjudge her pace or break her form, actually increasing the risk of injury.
And even though hill training is more efficient, it's much harsher than running the same distance on flat ground. The pain and exhaustion gnaw at an Uma Musume's spirit—so aside from obedient types like Mihono Bourbon, most avoid it.
…Wait. I think I heard in my past life that Uma Musume have formulas involving stamina and guts.
I didn't pay much attention back then—just thought "oh, okay" and forgot most details—but if that's true, it suddenly makes sense.
Pool training improves cardiovascular ability—stamina.
Hill training efficiently builds physical strength while reducing strain—and through the harsh load, improves racing grit.
That would explain a lot.
"Kuronuma-san."
"Thought of something?"
"How about hill training and pool training?"
"And why's that?"
"To extend distance—in other words, to run longer—pool training improves cardiovascular endurance for stamina, and hill training increases stepping strength and the related speed and grit through more efficient load without excessive strain.
When done with a proper schedule, both avoid overburdening the body."
"Not a bad judgement. You clearly understand the strengths of each training type. But your reasoning is from the perspective of a racing Uma Musume. If you want to become a trainer, you need to shift your viewpoint."
"A different… viewpoint?"
I instinctively echoed him. What kind of viewpoint change did he mean?
"Medical approaches are Minamisaka's specialty. If you want detailed explanations, ask her next time. For now, look at this."
He handed me a printed sheet. On it was an illustration—likely of an Uma Musume's leg. But not a normal diagram—more like a medical anatomical illustration, showing muscles and nerves intricately from thigh to toe.
"That's a copy from a medical textbook. Perfect for explanations.
Now—have you learned about muscle types from Minamisaka yet?"
"Muscles? No, like I said earlier at the smoking area, she's only taught me common topics like colds and basic symptoms."
"Then this'll be advance prep for next time. Muscles are broadly divided into three types. Know them?"
"Um… fast-twitch and slow-twitch, and… sorry, I forgot the last one."
"I said it earlier—what matters is not leaving unknown things unknown. You got two right. The last one is the intermediate muscle."
He circled parts of the diagram with a pen.
"First is white muscle—fast-twitch. As the name implies, it's pale. Thick fibers, fast contraction, strong explosive power, but poor endurance."
"I see…"
"Next is red muscle—slow-twitch. It's red. The fibers are thinner than fast-twitch. Explosive power is much lower, but because it relies on aerobic metabolism, endurance is far higher."
"A-aerobic metabolism?"
He moved to the whiteboard and wrote: white muscle, red muscle, intermediate muscle, aerobic metabolism. I copied everything into my notebook while listening.
"Right. Fast-twitch and slow-twitch use different energy sources. Slow-twitch uses aerobic metabolism—meaning it burns fats and carbs with enzymes for energy. Fast-twitch uses anaerobic glycolysis—breaking glucose into pyruvic acid and such for energy."
"So their energy sources differ…"
"Exactly. The 'aerobic exercise' you hear in dieting refers to exercise using slow-twitch muscles. Minamisaka knows more about this, so ask her if you want details."
"Understood."
"And the reason slow-twitch muscles are red is because they contain more myoglobin—a red oxygen-binding protein. Not the same as the hemoglobin in blood."
Even though he said Minamisaka was the expert, Kuronuma-san still shared small bits of knowledge. It made me feel warm inside.
"...Now then, I'll explain intermediate muscle later. But Nature—so far, have you noticed anything?"
He returned the pen to its holder and turned to me with the question.
What I've noticed…
With the explanation of explosive power and endurance earlier, I think I understood what he meant.
"Fast-twitch explosive power suits sprinters, slow-twitch endurance suits stayers—right?"
"Correct. But don't misunderstand. Stayers still need explosive power, and sprinters still need endurance."
"I know. I understand that."
"Good. Next—each person is born with different proportions of fast and slow muscles. That's true for Uma Musume and humans."
"Ehh!? Really!?"
"Yes. Meaning, in extreme terms, a stayer is born with more slow-twitch than fast-twitch, while a sprinter has more fast-twitch than slow-twitch."
His explanation genuinely shocked me. I'd heard of "people who build muscle easily and not easily" in my past life, but I never imagined it was determined from birth.
But then… doesn't that mean improving distance aptitude is nearly impossible? If you're born with a set proportion, you can't increase your slow-twitch muscles beyond that…
"To explain simply using game terms—imagine choosing a character with two equipment slots: one for fast-twitch, one for slow-twitch. Each slot has a set number of sub-slots.
A sprinter might have ten fast-twitch sub-slots and five slow-twitch ones.
A stayer would be the reverse."
"Mhm…"
"Total slot number is the same, but the ratios differ. You equip fast or slow muscles into their slots."
"But if the slots are fixed, you can't grow beyond them, right?"
He chuckled softly and sipped his coffee.
"Why do you think I used equipment slots as an analogy? Equipment can be upgraded in games nowadays, right?"
"You mean the muscles inside each slot can be strengthened, like leveling them up?"
"Exactly. If a muscle's max level is ten, the sprinter's slow-twitch slots give a max total of fifty. Let's call that stamina.
A stayer, with ten slow-slots, can reach a hundred."
"That sounds like a total lost cause…"
"It is. If they run at the same speed, a sprinter can never match a stayer in distance."
He drew a big X through the diagram.
"But Nature—there's one thing you forgot."
"?"
"This."
He circled "intermediate muscle" over and over.
"Like I said earlier, the proportion of muscle types is decided from birth. However, these intermediate fibers—were they formally called pink fibers…? Well, whichever—those are originally white fibers whose myoglobin was inactive, but through training they mutate and start carrying myoglobin. Because the myoglobin becomes active, they take on a reddish tint and become pink, which is the origin of the name.
"And the characteristic of these mutated intermediate fibers is that they possess the traits of both white and red muscles."
Kuronuma-san erased part of the board and began writing various terms and their explanations on the whiteboard. I hurried to copy each newly written word into my notebook.
"So, um… does that mean white fibers become intermediate fibers, and by strengthening them further, they become red fibers?"
"Unfortunately, intermediate fibers never become red fibers. They are, after all, white fibers that mutated, and they won't turn back into white fibers even if you stop using them."
"Ah… I see."
"And most importantly, although they carry the traits of both types, that doesn't mean they can match the explosive power of white fibers or the endurance of red fibers. Using the game example from earlier—if an intermediate fiber is level 10, then it would be like placing level 5 into explosive power and level 5 into endurance. It becomes a muscle whose performance sits right in the middle."
"So depending on how you look at it, it can be a jack-of-all-trades… or just mediocre at everything."
"That's right. For example, take that sprinter from earlier—out of their 10 white-fiber slots, say 5 mutated into intermediate fibers. The total white-fiber score of 100 would lose 25 points because 5 slots × level 5 becomes intermediate, dropping it to 75. But on the endurance side, it's the opposite: the red-fiber total is 50, and adding the intermediate 25 would bring it up to 75. With that, the gap between them and a stayer's stamina score—originally 50—narrows all the way to 25.
"If you can narrow the gap that much, even if long-distance races are still tough, doesn't it seem like a sprinter could easily compete in the mile or middle-distance races?"
"I—I think so."
That was all I could say as Kuronuma-san stepped away from the whiteboard and spoke to me directly. Maybe this is the difference between a trainer's perspective and that of a racing Uma Musume…
"…Of course, it has drawbacks. Intermediate fibers never revert to white fibers. Which means the total explosive power goes down. So it's entirely possible for a sprinter to lose their sprinter talent altogether."
He let out a small sigh, and for a moment, his words carried a quiet but unmistakable heaviness—like he was speaking from personal experience.
"And of course, your pool training is also important, just like you said. The fuel that powers the engine of an Uma Musume's body—her muscles—is oxygen. If the pumps that deliver that oxygen to the engine—your lungs and heart—are weak, then no matter how high-grade the engine is, it will never be able to show its full potential."
"Ah… thank you very much."
"Starting next time, if it's not raining like today, I'll teach you how much training on the hill course loads each part of the body, and how far you can safely push your current physique. If it rains, then it'll be classroom study like today."
"Yes! Please take care of me!"
"Let me make this clear—when we actually run, I'm watching from the warm-up onward, so don't start on your own. You're not even fully developed yet. If you put stress on yourself beforehand and end up with crush syndrome during hill training… what do you think Okino, O-Hana-san, or even the director would say to me? Honestly, I'd rather not imagine it."
"Yes, I understand."
The heavy atmosphere from earlier vanished completely. Kuronuma-san said all that in a tired tone. I mean, it's just the two of us here, so it's fine, but depending on how someone hears it, it might sound like I'm his assigned Uma Musume. I wonder if he realizes that?
Judging by the way he drinks his coffee with an exasperated look, probably not. If my status were that of an unassigned Uma Musume, I'd definitely misunderstand.
Why do male trainers—like in the app—say things that easily give Uma Musume the wrong idea…?
…No, I guess the app trainer and Okino-san are just weird. If I remember correctly, Okita Trainer in RTTT was actually a pretty decent person.
While I was thinking about such pointless things, I looked back at Kuronuma-san, only to find him already wiping the whiteboard clean and putting the pens away. It seemed today's lesson was over.
I packed my notebook and writing utensils into my bag, and downed the last of the coffee in my mug.
Even diluted, it was still a bit strong—and now halfway cold.
Honestly, it wasn't very good coffee. I carried my empty mug and Kuronuma-san's to the sink.
"I'll wash the cups. You should head back early."
His words made me finally notice it was already getting dark. We'd started late, but it seemed I'd been listening to him for quite a long time.
"I'm sorry. Thank you for today."
"Yeah. See you."
"Yes! Until next time."
I bowed deeply to Kuronuma-san, then used my bag as a makeshift umbrella and ran back to the dorm through the still-falling rain.
...
…When I rushed back to the dorm, I suddenly realized I'd left my uniform in the dryer inside Kuronuma-san's trainer room.
And so, with Rudolf-senpai sighing in disbelief, I had to run out into the rain all over again—but please, keep that part a secret.
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T/L:So long!!!(╯ರ ~ ರ)╯︵ ┻━┻